Charging a Two-Sphere
System by Induction Using a Negative Object
A GIF Animation
There are a variety of ways to charge an object. One such way is
known as induction. In the induction process, a charged object is
brought near but not touched to a neutral conducting object. The
presence of a charged object near a neutral conductor will force (or
induce) electrons within the conductor to move. The movement of
electrons leaves an unbalance of charge on opposite sides of the
neutral conductor. While the overall the object is neutral (i.e., has
the same number of electrons as protons), there is an excess of
positive charge on one side of the object and an excess of negative
charge on the opposite side of the object. Once the charge has been
separated within the object, a "ground" is brought near and touched
to one of the sides. The touching of the ground to the object permits
a flow of electrons between the object and the ground. The flow of
electrons results in a permanent charge being left upon the object.
When an object is charged by induction, the charge received by the
object is opposite the charge of the object which was used to charge
it.
The animation below depicts the induction process. Two neutral
conducting spheres rest on top of insulating stands. A negatively
charged balloon is brought near to (without touching) the left
sphere. The presence of the negatively-charged balloon forces
electron movement from the left sphere to the right sphere. This
movement of electrons is merely a reaction to the presence of
negatively-charged balloon (like charges repel). The result of the
rightward movement of electrons through the spheres is that the
spheres have become polarized. There is excess positive charge
on the left sphere and excess negative charge on the right sphere.
When the spheres are separated and the balloon is removed, the two
spheres display a charge. The left sphere ends up with a positive
charge (the opposite type of charge as the balloon). The right
sphere ends up with a negative charge.
During the induction process, there is never any movement of
electrons from the charged object to the spheres. The charged object
is only used to induce electron movement. Electrons, being negatively
charged, move about the conducting sphere as they are repelled by the
negatively-charged tube. These electrons move into the sphere on the
right which serves as a type of "ground" during the induction
process. Since there was a loss of negative charge in the form of
electrons from the left sphere, the overall charge on the left sphere
is positive. On the other hand, the right sphere having gained the
electrons has an overall negative charge. When the balloon is
removed, the excess charge on the two spheres becomes uniformly
distributed.
The induction process is characterized by the following general
features:
- A charged object is needed to charge an object by
induction. Yet there is never any contact made between the charged
object and the object being charged.
- Only conductors can be charged by the induction process.
The process relies on the fact that a charged object can force or
induce the movement of electrons about the material being
charged.
- The object being charged ends up with a charge which is the
opposite of the object being used to charge it.
- A ground must be used to create the charge on the
object. The ground allows for electron movement into or out of the
object being charged.
Additional information on physical descriptions of
electrostatic phenomenon will soon be available at
The
Physics Classroom.
This page was created by
Tom
Henderson of
Glenbrook South
High School.
Comments and suggestions can be sent by e-mail to
Tom
Henderson.
This page last updated on 2/9/98.